Piezoresistive transducer

ABSTRACT

A piezoresistive transducer is disclosed having a framework including a support element attached to a bending element that undergoes a deformation relative to the support element when a force acts on the bending element including a neutral fiber whose length does not change during the deformation. At least one piezoresistive expansion body is attached to the support element that exhibits a piezoresistive material and converts the deformation of the bending element into an electrically detectable change in resistance.

CROSS-REFERENCE TO RELATED APPLICATION

Reference is made to EP Application No. 10 2010 010 931.2, entitled“Piezoresistive Transducer”, filed on Mar. 10, 2011 andPCT/EP2011/00975, filed on Feb. 28, 2011, which applications areincorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

The invention relates to a piezoresistive transducer with a frameworkhaving a support element, attached to which is a bending element thatundergoes a deformation relative to the support element when a forceacts on it, which has a neutral fiber whose length does not changeduring the deformation, and attached to which is an expansion body thatexhibits a piezoresistive effect and converts the deformation of thebending element into an electrically detectable change in resistance.

DESCRIPTION OF THE PRIOR ART

There are numerous embodiments of transducers that convert mechanicalvariables, such as acceleration, force, expansion or pressure, into anelectrically detectable variable, such as, for example a change inresistance. One frequently employed principle here involves utilizingthe piezoresistive effect, in which the expansion of an expansion bodycomprised of electrically conductive or semiconducting material leads toa change in resistance of the latter. Out of physical necessity, allknown transducers of this type have at least one bending element formechanically recording the measured variable, at least one expansionbody as the piezoresistive element for converting the deformation of thebending element into an electrically detectable change in resistance,and at least one support. The aforementioned elements comprise amechanical framework that exhibits more or less complexity, depending onthe design. The transducers often also contain one or more additionalcounterweights that are attached to the bending element.

In the interests of providing a more comprehensible description, theframeworks described below will always be portrayed and explained usingprecisely one support element, precisely one bending element and anumber of piezoresistive elements. This does not imply that thefollowing descriptions do not encompass transducers with a frameworkmade up of several supports or several bending elements, or only one orespecially many piezoresistive elements, or all of these properties.

An expert is fully aware that strictly differentiating the framework ofpiezoresistive transducers into a support, a bending element and apiezoresistive element represents a simplification. All theabove-mentioned elements basically possess the inherent properties of abending element, that is, all of these elements have a limited rigidity,which counteracts a force that displaces the framework from of itsresting position. This fact notwithstanding, an expert can identify theindividual elements in a piezoresistive transducer, and delineate themfrom each other. For this reason, the strict separation between thementioned elements can be retained below, so that the principleunderlying the invention can thus be formulated with precision andclarity.

A piezoresistive transducer exhibits various quality features. The mostimportant feature is sensitivity, which indicates how much theresistance of the piezoresistive element changes at a given measuredvariable. Additional basic features include the mechanical stability,along with the lowest mechanical eigenfrequency of the framework, andhence the bandwidth of the transducer. The bandwidth of a transducerdetermines how high or low the variability of a measured variable canbe, so that the transducer can essentially correctly reflect thismeasured variable.

All metals and many semiconductors exhibit this piezoresistive effect.The latter is quantified for a given material by establishing the ratiobetween its relative change in resistance and its expansion. This ratiois referred to as the k-factor. A higher k-factor means that theresistance of a material is highly variable at a given expansion of thematerial, that is, the material is very sensitive. Metals have k-factorsranging from 2 to 6, while semiconductors can have k-factors that wellexceed 100. Therefore, it is advantageous to manufacture thepiezoresistive element of a piezoresistive transducer out of asemiconductor material like doped silicon, silicon carbide, diamond,gallium nitride, derivatives of gallium nitride or other III-Vsemiconductors, and seek a high k-factor in the process.

Among other things, the mechanical stability of a piezoelectrictransducer depends on how stably its individual elements are connectedwith each other and with the support. According to prior art, theframework comprised of a support, bending element and piezoresistiveelement can be connected either by joining techniques, such as adhesivebonding, bolting or related joining techniques, or the mentionedframework is monolithically fabricated. A monolithic composite ofindividual components implies that the stability of the joining surfacesof the sub-elements are only negligibly smaller than the stability ofany surface of the element as a whole. Negligibly implies that thesejoining surfaces do not constitute any predetermined breaking points.“Monolithic” can alternatively or additionally be any joining surfacebetween the sub-elements which is a uniform and direct atomic bond overthe entire joining surface, in terms of a covalent, ionic or metallicbond.

Monolithic fabrication is advantageous from the stability of thementioned framework, but not necessary, since weak spots that mightarise when joining individual sub-elements are avoided in this way.

In order to satisfy the requirement for a high sensitivity and highmechanical stability, numerous prior art piezoresistive transducers aremonolithically fabricated, with a piezoresistive element comprised of asemiconductor material having a high k-factor. For a given material,these transducers differ primarily in the geometry of the framework ofthe support, bending element and piezoresistive element. Thesedifferences in the geometry of the framework are determinative of thedifferences between the aforesaid piezoresistive transducers in terms ofquality features.

The prior art contains at least two geometric basic principles for theformation of a framework of a monolithic transducer fabricated with apiezoresistive element comprised of a semiconductor material. The firstprinciple will be briefly outlined with reference to the basic structureillustrated in FIG. 1 for the design of a piezoresistive transducer. Thepiezoresistive element is imbedded in the bending element 2, which isfixed on the support 3. The measured variable works in the direction ofthe arrow 4. The neutral fiber 6 of the bending element 2 is delineatedby way of orientation, and denotes the location at which compressive andtensile stresses within the bending element cancel each other out duringdeformation. An expert recognizes that use of the counterweight 5 isoptional, and does not change the geometric principle.

In the second principle illustrated in FIG. 3, the piezoresistiveelement 7 is an unsupported element between the support 3 and weight 5.Otherwise, the framework is designed identically to the one in FIG. 2.Attaching the piezoresistive element 7 as illustrated allows it to befixed in place further away from the neutral fiber 6, so that adistinctly higher expansion occurs along the piezoresistive element 7when exposed to the same measured variable 4 of the bending element 2 ason FIG. 2, making it possible to achieve a higher sensitivity given anidentical mechanical eigenfrequency.

To our knowledge, all known frameworks of monolithic piezoresistivetransducers equipped with a piezoresistive element comprised of asemiconductor material can be attributed to the two basic structuresdescribed above according to FIGS. 2 and 3. The first geometricprinciple is an industry standard because it is technically easy torealize, wherein there are countless embodiments thereof in existence.The second geometric principle is a great deal more complicated tofabricate due to the unsupported piezoresistive element, and thus is notas widespread.

The following publications each describe a piezoresistive accelerationsensor, which is based on the second principle elucidated above: U.S.Pat. Nos. 5,539,236, 4,605,919, and 4,689,600, U.S. PublishedApplication 2006/130596 and WO 9215018. In the known cases, two elementsarranged so that they can move relative to each other over a joiningregion with a narrowed design are joined together as a single piece, andhave arranged between them a kind of trench structure, which is bridgedby an expansion body consisting of a piezoresistive material. In U.S.Pat. Nos. 4,605,919 and 4,689,600, WO 92/15018 and U.S, PublishedApplication 2006/0117871, the piezoresistive expansion body spanning thetrench structure is largely unsupported, but is in all known casesoriented parallel to the neutral fiber of the bending element, whichrepresents the narrowed joining region between both movable elements.

SUMMARY OF THE INVENTION

The invention is a piezoresistive transducer with a framework having asupport element, attached to which is a bending element that undergoes adeformation relative to the support element when a force acts on it,which has a neutral fiber whose length does not change during thedeformation, and attached to which is an expansion body that exhibits apiezoresistive material which converts the deformation of the bendingelement into an electrically detectable change in resistance in such away as to make the transducer as sensitive as possible.

Already, the piezoresistive transducer according to FIG. 3, which isassembled based on the second principle explained above, was configuredwithin the framework of improving the sensitivity, that is, metrologicaldetectability of a deformation along the bending element caused byacceleration forces. As known, the change in electrical resistance in apiezoresistive element behaves monotonously to the expansion of thepiezoresistive element. That is, given an expansion of thepiezoresistive element in one direction, its electrical resistance alsochanges in only one direction. Therefore, the sensitivity of thepiezoresistive transducer is a maximal when the expansion of thepiezoresistive element is a maximal for a given measured variable. Forthis reason, the piezoresistive element serving as the expansion body isin the present case attached to a location of the framework geometrythat is exposed in relation to the potential expansion, that is, as faraway as possible from the bending element. However, this requires thatat least one extra auxiliary component or weight to be attached to thebending element to secure the expansion body.

The piezoresistive transducer concept basically makes use of the aboveknown concept, but dispenses with the necessity of providing anadditional component or weight joined with the bending element. Based onthe invention, a piezoresistive transducer has the support element andbending element at least regionally bordering a gap on at least twosides. At least one expansion body is provided, which locally joins thesupport element and bending element in the region of the gap in a bridgeand unsupported manner. The at least one expansion body has alongitudinal extension that intersects the neutral fiber of the bendingelement at an angle a ranging between 35° and 145°. It is particularlyadvantageous for the expansion body to be situated perpendicular to theneutral fiber, that is, α=90°.

As opposed to the previously known piezoresistive transducers and asexplained above, the expansion body does not extend along, that is,parallel to the neutral fiber of the bending element. Instead, it isunsupported relative to the neutral fiber of the bending element and isdisposed perpendicular thereto. However, this requires a special designof the framework, that is, the support element has the bending elementjoined thereto, which together bracket a gap with each other that isbridged by at least one expansion body. When an external force acts onthe framework to displace the bending element, the expansion body doesnot undergo any significant bending transverse to the expansion body'slongitudinal extension and is stretched or clinched along the expansionbody's longitudinal extension, resulting in a maximum electricallydetectable change in resistance. In the transducer according to theinvention, the expansion or deformation of the expansion body is greaterthan in the case of an expansion body oriented along the length of thebending element while exposed to an otherwise identical force. This isespecially the case since the displacement of the bending element isconverted directly into an expansion of the expansion body, occurringprimarily along its expansion body longitudinal extension, which isassociated with a maximum achievable electrically detectable change inresistance.

The expansion body preferably is made completely out of a transducermaterial, that is, a piezoresistive material, which ensures the highestpossible sensitivity in particular when the expansion body undergoes amaximum change in length while exposed to both expansion and clinching.This means that it has to be designed in such a way as to not experienceany evasive deformation, for example lateral bending, bulging or“snapping back”, transverse to the loading direction, in particularduring exposure to a clinching load. A potential evasive deformation canbe minimized by making the expansion body especially stable in designfrom a mechanical standpoint, for example giving it a small length tocross section ratio and/or using a particularly stable, if necessaryeven monolithically integratable material, such as silicon or othercrystalline materials.

It should be noted that the term “neutral fiber” does not need tonecessarily run inside the material or substance comprising the bendingelement or used in its manufacture. Bending element structures arepossible in which the neutral fiber also runs outside the actualmaterial of the bending element, in the form of a so-called virtualneutral fiber, for example in the case of a bending element structurehaving at least two braces running parallel to each other.

To further explain the piezoresistive transducer principle set upaccording to the invention, reference is made to the following exemplaryembodiments illustrated on the figures, whose specific configurationsare not intended to limit the general inventive idea.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be exemplarily described below based on exemplaryembodiments without limiting the general inventive idea, whereinreference is made to the drawings. Shown on:

FIG. 1 is a basic structure for describing a piezoresistive transduceraccording to the invention;

FIG. 2 is a schematic diagram of a transducer according to prior art;

FIG. 3 is a schematic diagram of a transducer according to prior art;

FIGS. 4 a and b illustrate a piezoresistive transducer with a bendingelement trilaterally joined with the support element;

FIG. 5 is a piezoresistive transducer with a bending elementunilaterally joined with the support element; and

FIG. 6 is a piezoresistive transducer with a bending elementunilaterally joined with the support element.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates a longitudinal section through the framework of apiezoresistive transducer according to the invention. The framework ofthe piezoresistive transducer has a stable support element 3, whoselongitudinal section is “L” shaped in design, with a short and long “L”leg 3′ and 3″. In the region of the short “L” leg 3′, the bendingelement 2 is unilaterally monolithically joined with the support element1, and is designed as a unilaterally securely clamped spring hanger. Inaddition, the bending element 2 with the longer “L” leg 1″ of thesupport structure 3 encompasses a gap S. In the region of the bendingelement edge 2′ that is frontally open-ended, an expansion body 1 of apiezoresistive material is provided between the support structure 3 andbending element 2′, which locally joins the support element 3 with thebending element 2. The expansion body 1 can be disk or pin-shaped indesign, and exhibits an expansion body longitudinal extension D that ispreferably oriented orthogonally to the neutral fiber 6 of the bendingelement 12. This applies in particular with respect to a bending element2 that is not displaced. Regardless of the design selected for theexpansion body, care must be taken that the latter is dimensionallystable transverse to its expansion body longitudinal extension, so thatload-induced transverse deformations can be precluded. This must also beobserved in particular when the expansion body is made entirely out of apiezoresistive material.

If the piezoresistive transducer is subjected to external accelerationforces, the surface elasticity exhibited by the bending element 2 causesit to deform as shown on FIG. 1, during which it is assumed that thebending element 2 becomes displaced relative to the rigid supportstructure 3 by a measured variable 4 to be acquired. The displacement ofthe bending element 2 causes the piezoresistive expansion body 1 toexpand along the expansion body longitudinal extension D, bringing abouta maximum detectable change in electrical resistance within theexpansion body.

According to the invention, the piezoresistive expansion body 1 isunsupported in design, from the standpoint that no additional supportbodies or support layers are provided for helping to join the supportstructure 3 and bending element 2 via the expansion body 1 preferablyexclusively or predominantly being a piezoresistive material. However,this does not explicitly rule out having additional elements with afunction other than mechanically supporting the piezoresistive expansionbody 1 be present in essentially the same location as the piezoresistiveelement. For example, these additional elements can be accessoryelements that influence the mechanical properties of the framework. Thisis once again referenced in conjunction with the exemplary embodimentshown on FIG. 5.

It is also easily possible that, with the bending element not beingdisplaced or deformed, the expansion body longitudinal extension D ofthe expansion body 1 and the neutral fiber 6 of the bending element 2includes an angle a that ranges between 45° and 135°, but preferablymeasures 90°.

FIGS. 4 a and b illustrate an embodiment of a piezoresistive transducerdesigned according to the invention. FIG. 4 a is a longitudinal sectionthrough the transducer arrangement, while FIG. 4 b shows a front view.It is assumed that the support structure 3 is square or cubical, andexhibits a rectangular trench structure G resembling a blind hole on asurface. A top view of the rectangular trench structure G is shown inFIG. 4 b. A disk-shaped bending element 2 is incorporated centrallyrelative to the trench structure G. The trailing edge 2″ and lateraledges 2″ are monolithically joined with the support structure 3, thatis, with the interior walls of the trench structure G. The disk-shapedbending element 2 is centrally arranged inside the trench structure G,and its bending element upper side and bending element lower side eachencompass a gap 3 with the support element 3. The bending element 2 alsoempties open ended at its front face 2′, which in the exemplaryembodiment according to FIG. 4 a and b forms a flush seal with thesurface of the support structure 3 with a top view of which is shown inFIG. 4 b.

Provided in the region of the frontally open-ended leading edge 2′ ofthe bending element 2 are expansion bodies 1 made out of apiezoresistive material, which are preferably designed as pins, and eachlocally join the support structure 3 with the bending element 2 at itsleading edge 2′. The pin-shaped piezoresistive expansion bodies 1 areeach arranged perpendicular to the upper and lower surface of thebending element 2, that is, perpendicular to the neutral fiber 6 (notdelineated) of the bending element 2, and each span the gap S. Inprinciple, any number of piezoresistive expansion bodies 1 which aredesired can be selected, wherein it is especially preferred to selectpiezoresistive expansion bodies 1 divided into groups of four, in whicha group of four contains two expansion bodies that join the upper sideof the bending element 2 with the support structure 3, as well as twoexpansion bodies 1 that join the lower side of the bending element 2with the support structure 3, as may be determined from the top viewaccording to FIG. 4 b (see dashed ellipses). All piezoresistiveexpansion bodies 1 belonging to a group of four are electricallyconnected to yield a Wheatstone bridge circuit, with which the smallestchanges in ohmic resistance can be ascertained. The piezoresistivetransducer illustrated on FIGS. 4 a and b is designed to acquireacceleration forces that are preferably oriented orthogonally to thesurface extension of the disk-shaped bending element 2. See the measuredvariable acting in the direction of arrow 4.

Another exemplary embodiment for a piezoresistive transducer isillustrated in FIG. 5, which compared to the top view of FIG. 4 b alsoshows a top view of a support structure 3, into which a trench structureG is incorporated in a similar manner. The bending element 2 illustratedin this embodiment is disk-shaped, and its open-ended leading frontaledge 2′ is visible. Let it be assumed further that the lateral edgelying to the rear and opposite the leading frontal edge 2′ ismonolithically joined with the support structure 3, while the twolateral edges 2″ of the bending element 2 of the leading frontal edge 2′are not joined with the support element 3. As a consequence, the bendingelement 2 must be regarded as a unilaterally clamped spring hanger,which causes the bending element 2 to have a far higher surfaceelasticity than in the case of the above exemplary embodiment, in whichthe bending element is trilaterally and monolithically joined with thesupport element. Therefore, the embodiment illustrated on FIG. 5exhibits a greater sensitivity in terms of detecting acceleration forcesat a lower mechanical eigenfrequency than does the embodiment shown inFIGS. 4 a and b.

In like manner, the piezoresistive expansion bodies 1 span the gap S ofthe trench structure G both between the upper surface of the bendingelement 2 with the support element 3 as well as between the lowersurface of the bending element 2 with the support element 3. A sectionalview of the embodiment illustrated on FIG. 5 will not be provided,especially since it is identical to the sectional view according to FIG.4 a.

FIG. 6 illustrates another embodiment, which differs from the embodimentillustrated on FIG. 5 in that only the lower gap S of the trenchstructure G is spanned by the piezoresistive expansion body 1. The upperpart 3* of the carrier element 3 is optional only, and can be readilyomitted.

FIG. 7 shows a further modification of the exemplary embodimentillustrated above on FIG. 6 which specifically is a longitudinalsectional view in which the frontal region of the bending element 2incorporates an additional weight M, which diminishes the mechanicaleigenfrequency of the piezoresistive transducer, and elevates thesensitivity in terms of detecting acceleration forces. While theadditional weight M is also able to deform the neutral fiber 6 extendingalong the bending element 2, the pin-shaped piezoresistive expansionbody 1 still extends largely perpendicular to the extension of theneutral fiber 6 which undergoes predominantly an expansion in theexpansion body longitudinal extension when the bending element 2 iscorrespondingly displaced, as a result of which a maximum detectablechange in resistance arises within the expansion body which can beacquired as a measured variable.

Aside from the specific exemplary embodiments described above forrealizing a piezoresistive transducer according to the invention, aplurality of other modifications are possible without having to alterthe geometric principle or the use of open-ended, piezoresistiveexpansion bodies made out of semiconductor material. For example, thesemodifications include adding another weight to any desired distributionor changing the shape of the support element or bending element, or theshape, number and location or spatial orientation of the piezoresistiveexpansion body. For example, a disk-shaped bending element along twoopposing lateral edges can be monolithically joined with the supportelement, while the remaining two opposing lateral edges of the otherwiserectangular disk-shaped bending element are open-ended. Even in thistype of embodiment, it is possible to provide piezoresistive expansionbodies on the two opposing, open-ended faces of the bending element inthe form according to the invention, specifically with a perpendicularexpansion body longitudinal extension of the neutral fiber of thedisk-shaped bending element. Another embodiment provides a disk-shapedbending element bordered by a circumferential edge that is circular,elliptical, or n-sided, or a hybrid of the above geometries. The bendingelement is here permanently joined over its entire circumferential edgewith the support element, and at least regionally spans the supportelement. At least one expansion body is situated between the supportelement and the bending element that spans the support element like amembrane. Such an embodiment is suitable for detecting higher orstronger acceleration forces.

The piezoresistive transducers designed according to the invention aresuitable for an especially advantageous manner of acquiringaccelerations or acceleration forces with a particularly pronounced,high sensitivity. To this end, use is advantageously made of measuredsignal acquisition by a Wheatstone measuring bridge, as depicted withreference to the exemplary embodiment according to FIG. 4 b or 5. Thebridge circuit has two pairs of resistors or takes the form of resistorcascades, which simultaneously are each exposed to an opposite but equalchange in resistance during the deflection or deformation of the bendingelement, which enables an especially precise measurement of the changein ohmic resistance.

The material along with the dimensions and shape of the framework, inparticular the support element, are preferably selected in such a way togive the piezoresistive transducer a high mechanical eigenfrequency,which is determined by the bending element. Preferred dimensions for therealization of piezoresistive transducers according to the inventionrange from tens to hundreds of pm. For example, the width of the bendingelement 2 in the exemplary embodiment according to FIG. 4 b comprises abending element thickness of 30 μm, a frontal edge length of 400 μm, aswell as a bending element length extending more deeply into the trenchstructure of 200 μm. The bending element 2 along with the supportstructure 3 here encompass a respective gap width S of 20 μm. The rod orpin-shaped piezoresistive expansion bodies according to FIGS. 4, 5, 6and 7 typically exhibit a diameter of 1 to 2 μm, and have an expansionbody longitudinal extension measuring at least the gap width of, forexample, 20 μm or more.

In a preferred embodiment, the piezoelectric transducer serves as ahigh-g acceleration sensor for acquiring accelerations of 1,000 g ormore, preferably of 100,000 g or more. In this case, properties relatingto sensitivity and mechanical eigenfrequency are of crucial importance.The mechanical rigidity, and hence the mechanical eigenfrequency,selected for the sensor must be high enough that even rapidly variableand very strong accelerations can be measured. In order to reach aneigenfrequency ranging from 1 to 3 MHz, and thereby obtain a timeresolution in the microsecond range for the measurement, the sensor mustbe fabricated on a microscale. The outer dimensions of the sensor liewithin a range of 1×2×1 mm (L×W×H), and yield a weight of about 5 mggiven the selection of silicon as the material. In order to achieve thehighest possible sensitivity at the required eigenfrequency, theextensively described aspects of the invention must be taken intoaccount in the process of designing the specific realizations, inparticular the geometric arrangement of the elements and the materialselection.

If the objective is to use this type of sensor as a high-g accelerationsensor, the latter, that is, the support element at least partiallyencompassing the at least one expansion body, is directly attached to ameasuring object, for example by way of adhesive bonding or some otherfixed joint. When logging the measured values, the support element isthus exposed to the entire acquirable acceleration effect that triggersthe corresponding deformation in the expansion body.

Especially preferably suited as the raw material for manufacturing apiezoresistive transducer designed according to the solution is silicon,which is processed in a suitable form using known manufacturing andprocessing methods from semiconductor technology.

REFERENCE LIST

-   1 Expansion body-   2 Bending element-   2′ Leading edge of the bending element-   2″ Trailing edge of the bending element-   2′″ Lateral edges of the bending element-   3 Support element-   3′ Short L-leg of the support element-   3″ Long L-leg of the support element-   4 Exposure to external force, acceleration force-   5 Additional weight-   6 Neutral fiber-   D Expansion body longitudinal extension-   M Additional weight-   G Trench structure-   S Gap

1-15. (canceled)
 16. A piezoresistive transducer comprising: a framework including a support element, a bending element attached to the support element which undergoes a deformation relative to the support element when a force acts on the bending element, the bending element including a neutral fiber whose length does not change during the deformation and the bending element being attached to at least one expansion body and comprising a piezoresistive material which converts the deformation of the bending element into an electrically detectable change in resistance; and wherein the support element and bending element at least border a gap on at least two sides, the gap contains the at least one expansion body that joins the support element and the bending element into an electrical bridge circuit which is unsupported and that the at least one expansion body has a longitudinal extension which intersects the neutral fiber at an angle a ranging between 35°≦α≦145°.
 17. The piezoresistive transducer according to claim 16, wherein: the at least one expansion body is permanently joined to the support element and the bending element.
 18. The piezoresistive transducer according to claim 16, wherein: the bending element and at least one expansion body are monolithically joined, or the support element, bending element and expansion body are monolithically joined.
 19. The piezoresistive transducer according to claim 17, wherein: the bending element and at least one expansion body are monolithically joined, or the support element, bending element and expansion body are monolithically joined.
 20. The piezoresistive transducer according to claim 16, wherein: the bending element comprises a pin or disk including at least two opposing lateral edges, one lateral edge being permanently joined with the support element and another lateral edge being open ended; and the at least one expansion body is disposed on or proximate to the open-ended lateral edge between the support element and bending element.
 21. The piezoresistive transducer according to claim 17, wherein: the bending element comprises a pin or disk including at least two opposing lateral edges, one lateral edge being permanently joined with the support element and another lateral edge being open ended; and the at least one expansion body is disposed on or proximate to the open-ended lateral edge between the support element and bending element.
 22. The piezoresistive transducer according to claim 18, wherein: the bending element comprises a pin or disk including at least two opposing lateral edges, one lateral edge being permanently joined with the support element and another lateral edge being open ended; and the at least one expansion body is disposed on or proximate to the open-ended lateral edge between the support element and bending element.
 23. The piezoresistive transducer according to claim 19, wherein: the bending element comprises a pin or disk including at least two opposing lateral edges, one lateral edge being permanently joined with the support element and another lateral edge being open ended; and the at least one expansion body is disposed on or proximate to the open-ended lateral edge between the support element and bending element.
 24. The piezoresistive transducer according to claim 16, wherein: the bending element comprises a disk and is bordered by four lateral edges, the bending element is permanently joined with the support element by two opposed lateral edges and two other lateral edges which are open-ended; and the at least one expansion body is on or proximate to at least one open-ended lateral edge between the support element and bending element.
 25. The piezoresistive transducer according to claim 17, wherein: the bending element comprises a disk and is bordered by four lateral edges, the bending element is permanently joined with the support element by two opposed lateral edges and two other lateral edges which are open-ended; and the at least one expansion body is on or proximate to at least one open-ended lateral edge between the support element and bending element.
 26. The piezoresistive transducer according to claim 18, wherein: the bending element comprises a disk and is bordered by four lateral edges, the bending element is permanently joined with the support element by two opposed lateral edges and two other lateral edges which are open-ended; and the at least one expansion body is on or proximate to at least one open-ended lateral edge between the support element and bending element.
 27. The piezoresistive transducer according to claim 19, wherein: the bending element comprises a disk and is bordered by four lateral edges, the bending element is permanently joined with the support element by two opposed lateral edges and two other lateral edges which are open-ended; and the at least one expansion body is on or proximate to at least one open-ended lateral edge between the support element and bending element.
 28. The piezoresistive transducer according to claim 16, wherein: the bending element comprises a disk and includes an upper and lower side; the support element is spaced relative to the bending element so that the bending element and the support element borders two gaps with one gap being between the upper side of the bending element and the support element and another gap being spaced relative to the lower side of the bending element and the support element; the bending element comprises at least two opposing lateral edges, one lateral edge being permanently joined with the support element and another lateral edge being open-ended or the bending element is permanently joined with the support element by two opposing lateral edges, and comprising two additional lateral open-ended edges; and the at least one expansion body is disposed on or in proximity to at least one open-ended lateral edge between the support element and the bending element.
 29. The piezoresistive transducer according to claim 17, wherein: the bending element comprises a disk and includes an upper and lower side; the support element is spaced relative to the bending element so that the bending element and the support element borders two gaps with one gap being between the upper side of the bending element and the support element and another gap being spaced relative to the lower side of the bending element and the support element; the bending element comprises at least two opposing lateral edges, one lateral edge being permanently joined with the support element and another lateral edge being open-ended or the bending element is permanently joined with the support element by two opposing lateral edges, and comprising two additional lateral open-ended edges; and the at least one expansion body is disposed on or in proximity to at least one open-ended lateral edge between the support element and the bending element.
 30. The piezoresistive transducer according to claim 18, wherein: the bending element comprises a disk and includes an upper and lower side; the support element is spaced relative to the bending element so that the bending element and the support element borders two gaps with one gap being between the upper side of the bending element and the support element and another gap being spaced relative to the lower side of the bending element and the support element; the bending element comprises at least two opposing lateral edges, one lateral edge being permanently joined with the support element and another lateral edge being open-ended or the bending element is permanently joined with the support element by two opposing lateral edges, and comprising two additional lateral open-ended edges; and the at least one expansion body is disposed on or in proximity to at least one open-ended lateral edge between the support element and the bending element.
 31. The piezoresistive transducer according to claim 19, wherein: the bending element comprises a disk and includes an upper and lower side; the support element is spaced relative to the bending element so that the bending element and the support element borders two gaps with one gap being between the upper side of the bending element and the support element and another gap is spaced relative to the lower side of the bending element and the support element; the bending element comprises at least two opposing lateral edges, one lateral edge being permanently joined with the support element and another lateral edge being open-ended or the bending element is permanently joined with the support element by two opposing lateral edges and two additional lateral edges are open-ended; and the at least one expansion body is disposed on or in proximity to at least one open-ended lateral edge between the support element and the bending element.
 32. The piezoresistive transducer according to claim 28, wherein: at least two expansion bodies are disposed between the upper side of the bending element and the support element; and at least two expansion bodies are disposed between the lower side of the bending element and the support element and at least four expansion bodies are connected in a Wheatstone bridge.
 33. The piezoresistive transducer according to claim 29, wherein: at least two expansion bodies are disposed between the upper side of the bending element and the support element; and at least two expansion bodies are disposed between the lower side of the bending element and the support element and at least four expansion bodies are connected in a Wheatstone bridge.
 34. The piezoresistive transducer according to claim 30, wherein: at least two expansion bodies are disposed between the upper side of the bending element and the support element; and at least two expansion bodies are disposed between the lower side of the bending element and the support element and at least four expansion bodies are connected in a Wheatstone bridge.
 35. The piezoresistive transducer according to claim 31, wherein: at least two expansion bodies are disposed between the upper side of the bending element and the support element; and at least two expansion bodies are disposed between the lower side of the bending element and the support element and at least four expansion bodies are connected in a Wheatstone bridge.
 36. The piezoresistive transducer according to claim 16, wherein: the bending element comprises a disk bordered by a circumferential edge; the bending element is permanently joined with the support element over the circumferential edge and at least regionally spans the support element as a membrane; and the at least one expansion body is defined between the support element and the bending element that spans the support element as a membrane.
 37. The piezoresistive transducer according to claim 17, wherein: the bending element comprises a disk bordered by a circumferential edge; the bending element is permanently joined with the support element over the circumferential edge and at least regionally spans the support element as a membrane; and the at least one expansion body is defined between the support element and the bending element that spans the support element as a membrane.
 38. The piezoresistive transducer according to claim 18, wherein: the bending element comprises a disk bordered by a circumferential edge; the bending element is permanently joined with the support element over the circumferential edge and at least regionally spans the support element as a membrane; and the at least one expansion body is defined between the support element and the bending element that spans the support element as a membrane.
 39. The piezoresistive transducer according to claim 19, wherein: the bending element comprises a disk bordered by a circumferential edge; the bending element is permanently joined with the support element over the circumferential edge and at least regionally spans the support element as a membrane; and the at least one expansion body is defined between the support element and the bending element that spans the support element as a membrane.
 40. The piezoresistive transducer according to claim 16, wherein: a weight is provided on the bending element which influences oscillation or rigidity of the bending element.
 41. The piezoresistive transducer according to claim 17, wherein: a weight is provided on the bending element which influences oscillation or rigidity of the bending element.
 42. The piezoresistive transducer according to claim 18, wherein: a weight is provided on the bending element which influences oscillation or rigidity of the bending element.
 43. The piezoresistive transducer according to claim 19, wherein: a weight is provided on the bending element which influences oscillation or rigidity of the bending element.
 44. The piezoresistive transducer according to claim 20, wherein: a weight is provided on the bending element which influences oscillation or rigidity of the bending element.
 45. The piezoresistive transducer according to claim 24, wherein: a weight is provided on the bending element which influences oscillation or rigidity of the bending element.
 46. The piezoresistive transducer according to claim 28, wherein: a weight is provided on the bending element which influences oscillation or rigidity of the bending element.
 47. The piezoresistive transducer according to claim 32, wherein: a weight is provided on the bending element which influences oscillation or rigidity of the bending element.
 48. The piezoresistive transducer according to claim 36, wherein: a weight is provided on the bending element which influences oscillation or rigidity of the bending element.
 49. The piezoresistive transducer according to claim 16, wherein: a longitudinal extension of the expansion body extends in a spatial direction along which the expansion body deforms which influences the electrically detectable change in resistance of the bridge.
 50. The piezoresistive transducer according to claim 16, wherein: the support element, bending element and expansion element comprise semiconductors.
 51. The piezoresistive transducer according to claim 17, wherein: the at least one expansion body comprises a piezoresistive material which is extensible, is attached along a longitudinal extension of the at least one expansion body and is not dimensionally extensible transverse to the longitudinal extension.
 52. An acceleration sensor for sensing accelerations of at least 1,000 g comprising: a framework including a support element, a bending element attached to the support element which undergoes a deformation relative to the support element when a force acts on the bending element, the bending element including a neutral fiber whose length does not change during the deformation and the bending element being attached to at least one expansion body and comprising a piezoresistive material which converts the deformation of the bending element into an electrically detectable change in resistance; and wherein the support element and bending element at least border a gap on at least two sides, the gap contains the at least one expansion body that joins the support element and the bending element into an electrical bridge circuit which is unsupported and that the at least one expansion body has a longitudinal extension which intersects the neutral fiber at an angle a ranging between 35°≦α≦145°.
 53. The acceleration sensor according to claim 52, wherein: the support element at least partially surrounds the bending element and the at least one expansion body and is joined to a measuring device exposed to an acceleration acting on at least one exterior side of the support element.
 54. The acceleration sensor according to claim 53, wherein: the support element, the bending element and the at least one expansion body comprise a volume of 1 to 10 mm³.
 55. The acceleration sensor according to claim 54, wherein: the volume comprises 1 to 3 mm³. 